Seeing how in 2000 & 2004 a lot of teams used some sort of hook or over the bar latching type mechanism here would be my suggestions for a standard:
1.
SOMEWHERE on your robot put a bar that is the same OD as the 1.5" x.083 Wall 1020 CRS DOM Tube, and if possible use the same material.
Make the decision of WHERE to put it based on YOUR robot design. It shouldn't really matter to the other robots unless they have preprogrammed heights (in which case they or you can reprogram it for where your bar will be!) and as long as it is the right OD and strong enough to hold a 120lb robot, it will work and will be reasonably universal. If you wanted to get real fancy, put one on either side, so its easier to hang 2 robots off you.
2.
Leave at LEAST 10" of free space between your mounting brackets.
This will give teams enough to "grab onto" and will account for different mechanisms. If you can leave even more room (ie put the mounting on the corners of your robot frame) its much more likely you could get 2 robots to hang off of you.
3.
Make sure YOUR elevation mechanism can handle 300-450lbs hanging off of it. You may not need to LIFT this much if you get in place and let the other robots latch onto you, but you need to SUPPORT that much weight.
4.
Paint it Bright Green. No vision target lights this year, so we are free to use whatever color, and that will be the most viewable from a distance. (Got this idea from a previous post
)
And really, that should be enough of a standard.